The endothelial cell very likely plays a key role in the pathogenesis of diabetic microvascular disease. Despite this, little is known about fuel metabolism in the normal endothelial cell and nothing is known about the effect of diabetes. We have recently demonstrated that glucose oxidation and lactate release are depressed in cerebral microvessels (mainly capillaries plus some arterioles and venules) from diabetic rats, suggesting that the endothelial cell may be sensitive to insulin lack. The principal objective of this proposal is to expand upon these observations, and in particular to characterize the regulation of fuel metabolism in the endothelial cell and how it is affected by insulin. The studies will primarily utilize capillary and arteriole-enriched microvessel preparations from rat brain. The uptake and disposition of glucose, free fatty acids and ketone bodies, and the activities of a number of insulin-sensitive enzymes will be assessed in microvessels from control and diabetic rats. In addition, the biological effects of insulin, insulin binding and the transport of ions and hexoses will be evaluated. To determine whether cerebral capillaries are metabolically unique, similar studies will be performed using capillaries from adipose tissue and the retina. These studies should enhance our understanding of the metabolic and functional events in the endothelial cell which antedate and perhaps contribute to the development of vascular complications in the diabetic. In addition, they should help to establish whether alterations in these cells could contribute to the pathogenesis of central nervous system dysfunction in ketoacidosis and other diabetes-related encephalopathies.